1. Field of the Invention
The present invention relates to an apparatus and method for driving an ink-jet printhead. More particularly, the present invention relates to an apparatus and method for driving a thermal ink-jet printhead that is able to extend a lifespan of a heater by alternately applying current pulses to the heater.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of ink at a desired position on a recording sheet. Ink-jet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermal ink-jet printhead, in which a heat source is employed to form and expand a bubble in ink to cause an ink droplet to be ejected due to the expansive force of the formed bubble. A second type is a piezoelectric ink-jet printhead, in which an ink droplet is ejected by a pressure applied to the ink due to a deformation of a piezoelectric element.
An ink droplet ejection mechanism of a thermal ink-jet printhead will now be explained in detail. When a current pulse is supplied to a heater, which includes a heating resistor, the heater generates heat and ink near the heater is instantaneously heated to approximately 700° C., thereby boiling the ink. The boiling of the ink causes bubbles to be generated and exert pressure on ink filling an ink chamber. As a result, ink around a nozzle is ejected from the ink chamber in the form of a droplet through the nozzle.
A thermal inkjet printhead is classified into a top-shooting type, a side-shooting type, and a back-shooting type depending on a bubble growing direction and a droplet ejection direction. In a top-shooting type of printhead, bubbles grow in the same direction in which an ink droplet is ejected. In a side-shooting type of printhead, bubbles grow in a direction perpendicular to a direction in which an ink droplet is ejected. In a back-shooting type of printhead, bubbles grow in a direction opposite to a direction in which an ink droplet is ejected.
An ink-jet printhead using the thermal driving method should satisfy the following requirements. First, manufacturing of the ink-jet printheads should be simple, costs should be low, and should facilitate mass production thereof. Second, in order to obtain a high-quality image, cross talk between adjacent nozzles should be suppressed while a distance between adjacent nozzles should be narrow; that is, in order to increase dots per inch (DPI), a plurality of nozzles should be densely positioned. Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after being ejected from the ink chamber should be as short as possible and the cooling of heated ink and heater should be performed quickly to increase an operating frequency.
FIG. 1 illustrates an exploded perspective view of a conventional thermal ink-jet printhead. FIG. 2 illustrates a cross-sectional view for explaining a process of ejecting an ink droplet using the conventional thermal ink-jet printhead of FIG. 1.
Referring to FIGS. 1 and 2, the conventional thermal ink-jet printhead includes a substrate 10, an ink chamber 26, which is formed on the substrate 10 and stores ink therein, partition walls 14, which define the ink chamber 26, a heater 12, which is disposed within the ink chamber 26, a nozzle 16, through which an ink droplet 29′ is ejected, and a nozzle plate 18, through which the nozzle 16 is formed. In operation, a current pulse is supplied to the heater 12 to generate heat, such that ink 29 filled in the ink chamber 26 is heated, thereby generating a bubble 28. The generated bubble 28 is continuously expanded such that pressure is applied to the ink 29 filled in the ink chamber 26, thereby ejecting the ink droplet 29′ out of the printhead through the nozzle 16. Subsequently, ink 29 from a manifold 22 is introduced into the ink chamber 26 through an ink channel 24. Resultantly, the ink chamber 26 is refilled with ink 29.
FIG. 3 is a circuit diagram of a first conventional circuit for driving a thermal ink-jet printhead. FIG. 4 is a diagram illustrating pulses of the first conventional circuit of FIG. 3.
Referring to FIGS. 3 and 4, in a circuit to which a positive voltage V1 is constantly applied as a supply voltage pulse VCC to drive an ink-jet printhead, a current pulse IH is supplied to a thin film heater 30 using a drive signal SDR and a field effect transistor (FET). According to the conventional circuit, since a current flows in a constant direction through the heater 30, damage to the heater 30 may occur due to electromigration. Recently, attempts to reduce an amount of energy applied to a high-density printhead by reducing a thickness of a heater therein have been made. As the heater becomes thinner, however, damage to the heater due to electromigration becomes a more serious problem.
FIG. 5 is a circuit diagram of a second conventional circuit for driving an ink-jet printhead. FIG. 6 is a diagram illustrating pulses of the second conventional circuit of FIG. 5.
Referring to FIGS. 5 and 6, in a circuit to which a supply voltage pulse VCC is supplied to drive an ink-jet printhead, a current pulse IH is supplied to a heater 50 using a drive signal SDR and a driving electric FET. A current waveform is controlled by means of a pull down resistor and two electric FETs. According to the second conventional circuit, current waveform distortion, such as overshoot, may be reduced, and thus maximum current amplitude is lowered, which results in a decrease in damage to the heater 50 due to electromigration. As mentioned above, the second conventional circuit similarly has a similar in reducing the possibility of damage to the heater 50 that is caused by a decrease in a thickness of the heater 50.